1. Field of the Invention
The present invention relates to logic converters, i.e., circuits for converting digital input signals of one logic type to digital output signals of another logic type. In particular, the invention relates CMOS logic converters for converting digital input signals to CMOS digital output signals.
2. State of the Art
A number of integrated circuit technologies, or logic families, have been developed, each having its own characteristics in terms of speed and power. Emitter-Coupled Logic (ECL) is the fastest logic commercially available in silicon. The speed of ECL is obtained at the price of high power dissipation. Nevertheless, where high-speed computation is a necessity, ECL may be used to advantage. Complimentary Metal Oxide Semiconductor (CMOS) technology, on the other hand, exhibits very low power dissipation but only moderate speed. CMOS also allows high integration densities to be achieved, making it the preferred technology for Very Large Scale Integration (VLSI). Transistor Transistor Logic (TTL) falls in between ECL and CMOS in terms of speed and power. By changing the values of resistors, a trade off between speed and power may be made.
Logic converters are used to enable integrated circuits of different logic families to be used together. Logic converters are known that convert ECL signals to CMOS signals, as are logic converters that convert TTL signals to CMOS signals. Such logic converters have been embodied in separate parts. Stocking separate parts increases inventory costs.
A need therefore exists for a logic converter to enable a product to work with either an ECL signal input or a TTL signal input without the need of modifying the product or of reconfiguring the product in any way. Such a product could be incorporated in either a high-speed high-performance system (i.e., ECL logic) or a lower-speed lower-cost system (i.e., TTL logic), according to the choice of the user.